1st mob to the left when you enter is a Caster.

I doesnt really matter what gear you have when trying to kill a caster mob since their dmg simply ignore anything but resistance or dmg reduction talents.

and nexxus mobs are of sufficient lvl to give you a hard time since they are elite dungeon mobs, so dont worry your gear is enough, but also since you are a warrior, use kick etc to interupt it.